Chemical and electrochemical methods are known for the synthesis of diaryliodonium salts. U.S. Pat. No. 3,885,036 discloses the preparation of a mixed heterocyclic/carbocyclic iodonium compound, specifically 4-chlorophenyl-2-thienyliodonium salt, by reacting the iodosyl compound, isolated and purified 4-chloroiodosobenzene diacetate, with thiophene and an anion source. The method disclosed in U.S. Pat. No. 3,885,036, however, requires a separate quantity of peracid in order to prepare the iodosyl compound or the use of toxic lead compounds. Subsequent isolation and purification of the iodosyl compound is expensive and poses significant risk of spontaneous detonation as unstable and explosive iodoxyl compounds may be formed.
U.S. Pat. No. 5,277,767 discloses a method for electrochemically synthesizing diaryl iodonium salts in an undivided cell utilizing carbon electrodes, acetic acid as the solvent, and sulfuric acid as the electrolyte. However, only aryl compounds resistant to oxidation/decomposition in the presence of an electric current are suitable for use as a target aryl compound.
Known conventional electrochemical processes for the formation of diaryliodonium salts from benzene or toluene and iodobenzene utilizing divided cells have proven to be commercially impractical as a high voltage drop is involved in these processes. The semi-permeable membranes associated with divided cell use are also problematic. These processes also require expensive platinum electrodes, further diminishing the appeal of employing such methods.
A need exists for a method of producing diaryl iodonium compounds that does not require large amounts of concentrated and unstable starting reagents such as peracids and/or peroxides and also eliminates the hazards associated with the isolation and purification of iodosyl compounds. A need further exists for a method of producing diaryl iodonium compounds which accommodates labile target aryl compounds sensitive to degradation when exposed to oxidizing and reducing environments in an undivided electrochemical cell.